The quantitative determination of amylase in physiologic fluids is widely accepted as an index of pancreatic dysfunction but suffers from a lack of specificity due to the existence of multiple molecular forms and extrapancreatic sources of this enzyme (isoamylases). In spite of the extensive evidence that human isoamylases exist, the biochemical basis and tissue origins of human isoamylases have not been completely elucidated. Human Isoamylases, first of pancreatic and salivary origins and later of other tissues, will be isolated and purified. The isolated enzymes will be physiochemically, catalytically, and immunochemically characterized. Amino acid substitutions are anticipated among the various isoamylases; thus extensive amino acid and peptide analytic investigations are anticipated to include amino acid sequence investigations of the major isoamylases.